I think, if possible, it should be done before chapter 4 comes out. I know it means that we'll have to wait for the new chapter, but hear me out here.
Let's say chapter 4 comes out tomorrow. The masses rejoice, the land is fertile again, the blind recover eyesight, babies laugh, politicians give the money back to the people, the world is right anew. Then what happens? New peeps come here and wonder why we few, we happy few, sing the praises of Heavy Five and the Great Notty (blessed be Her name). So the new peeps download the game, and the first thing they see are these grainy renders! They close the game, delete it and leave forever wondering why we're so crazy about it.
Now, in this new paradigm, it all starts the same, except chapter 4's out later. People rejoice, politicians find they have a heart, etc. And the newbies come to us with shiny faces and *innocent* expectations. They download the first chapters and BAM!! Quality! Quality everywhere!
I guarantee you the tread will be flooded with "wy didn't i downloaded that game before?!?" Ok, it might become tedious, but think about the sweet patreon money that will go directly into Notty's beaver hamster...
Also, in a more serious tone, if Notty does indeed intend for the base to have a new face, it would be weird to either have the new graphics in chapter 4 but not the old ones or, worse, to keep going until she finally makes the decision to work on the remaster, but this time, the amount of work will be greater.
Just food for thought